Because LCDs have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, etc.
A conventional LCD typically includes a liquid crystal (LC) panel, a backlight module with a plurality of light sources for illuminating the LC panel, and a backlight modulation circuit for modulating illumination provided by the backlight module.
Referring to FIG. 3, this depicts one embodiment of an analog method for modulating illumination provided by a backlight module of an LCD. In the analog method, as a voltage level for a driving voltage increases, the illumination provided by the backlight module also increases. Likewise, as the voltage level for the driving voltage decreases, the illumination provided by the backlight module also decreases.
In a digital method for modulating illumination provided by a backlight module, pulse width modulation (PWM) and pulse frequency modulation (PFM) may be used. FIG. 4 depicts one embodiment of a PWM method for modulating illumination provided by a backlight module. In the PWM method, a duty ratio of a pulse voltage signal is changed in order to modulate the illumination provided by the backlight module. When the duty ratio increases, the illumination provided by the backlight module also increases. Similarly, when the duty ratio decreases, the illumination provided by the backlight module also decreases.
One drawback of the above-described analog and digital PWM methods is that they can only modulate the illumination provided by the backlight module little by little. However, if an LCD needs to be modulated in both a large range and a precise range, then many modulation commands and signals may need to be analyzed. In such case, modulating the many commands and signals wastes valuable processor cycles and consumes additional energy.
It is desired to provide a backlight modulation circuit which can overcome the above-described deficiencies.